diff --git a/src/libslic3r/Config.cpp b/src/libslic3r/Config.cpp
index 63e2b3821e..3f0b500c42 100644
--- a/src/libslic3r/Config.cpp
+++ b/src/libslic3r/Config.cpp
@@ -904,6 +904,10 @@ size_t ConfigBase::load_from_gcode_string_legacy(ConfigBase& config, const char*
         end = start;
     }
 
+    // Do legacy conversion on a completely loaded dictionary.
+    // Perform composite conversions, for example merging multiple keys into one key.
+    config.handle_legacy_composite();
+
     return num_key_value_pairs;
 }
 
@@ -1073,6 +1077,10 @@ ConfigSubstitutions ConfigBase::load_from_gcode_file(const std::string &filename
 
     if (key_value_pairs < 80)
         throw Slic3r::RuntimeError(format("Suspiciously low number of configuration values extracted from %1%: %2%", filename, key_value_pairs));
+
+    // Do legacy conversion on a completely loaded dictionary.
+    // Perform composite conversions, for example merging multiple keys into one key.
+    this->handle_legacy_composite();
     return std::move(substitutions_ctxt.substitutions);
 }
 
@@ -1114,6 +1122,9 @@ ConfigSubstitutions ConfigBase::load_from_binary_gcode_file(const std::string& f
         this->set_deserialize(key, value, substitutions_ctxt);
     }
 
+    // Do legacy conversion on a completely loaded dictionary.
+    // Perform composite conversions, for example merging multiple keys into one key.
+    this->handle_legacy_composite();
     return std::move(substitutions_ctxt.substitutions);
 }
 
diff --git a/src/libslic3r/GCode/Thumbnails.cpp b/src/libslic3r/GCode/Thumbnails.cpp
index 6e2b51f764..0e088d0368 100644
--- a/src/libslic3r/GCode/Thumbnails.cpp
+++ b/src/libslic3r/GCode/Thumbnails.cpp
@@ -192,7 +192,7 @@ std::string get_error_string(const ThumbnailErrors& errors)
     std::string error_str;
 
     if (errors.has(ThumbnailError::InvalidVal))
-        error_str += "\n - " + format("Invalid input format. Expected vector of dimensions in the following format: \"%1%\"", "XxYxEXT, XxYxEXT, ...");
+        error_str += "\n - " + format("Invalid input format. Expected vector of dimensions in the following format: \"%1%\"", "XxY/EXT, XxY/EXT, ...");
     if (errors.has(ThumbnailError::OutOfRange))
         error_str += "\n - Input value is out of range";
     if (errors.has(ThumbnailError::InvalidExt))
diff --git a/src/libslic3r/PrintConfig.cpp b/src/libslic3r/PrintConfig.cpp
index e7c05e8db0..4ac981c960 100644
--- a/src/libslic3r/PrintConfig.cpp
+++ b/src/libslic3r/PrintConfig.cpp
@@ -310,7 +310,7 @@ void PrintConfigDef::init_common_params()
 
     def = this->add("thumbnails", coString);
     def->label = L("G-code thumbnails");
-    def->tooltip = L("Picture sizes to be stored into a .gcode and .sl1 / .sl1s files, in the following format: \"XxYxEXT, XxYxEXT, ...\"");
+    def->tooltip = L("Picture sizes to be stored into a .gcode and .sl1 / .sl1s files, in the following format: \"XxY/EXT, XxY/EXT, ...\"");
     def->mode = comExpert;
     def->gui_type = ConfigOptionDef::GUIType::one_string;
     def->set_default_value(new ConfigOptionString());
diff --git a/src/slic3r/GUI/Field.cpp b/src/slic3r/GUI/Field.cpp
index e82f835587..5be4434211 100644
--- a/src/slic3r/GUI/Field.cpp
+++ b/src/slic3r/GUI/Field.cpp
@@ -382,7 +382,7 @@ void Field::get_value_by_opt_type(wxString& str, const bool check_value/* = true
                 set_value(str_out, true);
                 wxString error_str;
                 if (errors.has(ThumbnailError::InvalidVal))
-                    error_str += format_wxstr(_L("Invalid input format. Expected vector of dimensions in the following format: \"%1%\""), "XxYxEXT, XxYxEXT, ...");
+                    error_str += format_wxstr(_L("Invalid input format. Expected vector of dimensions in the following format: \"%1%\""), "XxY/EXT, XxY/EXT, ...");
                 if (errors.has(ThumbnailError::OutOfRange)) {
                     if (!error_str.empty())
                         error_str += "\n\n";