Courtesy of Yann:

Bugfix: Special registers for address mode matching only worked with lower case register names.
Bugfix: movem with pc-relative mode was missing for weird immediate mode.
Bugfix: btst with pc-relative and weird immediate mode was missing.
Enhancement: Assembler syntax with implicit immediate 1 for shifts and rotations no longer cause syntax errors.

src/main/resources/META-INF/plugin.xml

@@ -16,7 +16,7 @@
 
     <extensions defaultExtensionNs="com.intellij">
         <fileType name="MC68000 Assembler" implementationClass="de.platon42.intellij.plugins.m68k.M68kFileType"
-                  fieldName="INSTANCE" language="MC68000" extensions="asm;ASM;s;S;i"/>
+                  fieldName="INSTANCE" language="MC68000" extensions="asm;s;i"/>
         <lang.parserDefinition language="MC68000"
                                implementationClass="de.platon42.intellij.plugins.m68k.parser.M68kParserDefinition"/>
         <lang.syntaxHighlighterFactory language="MC68000"
@@ -47,7 +47,7 @@
         <stubIndex implementation="de.platon42.intellij.plugins.m68k.stubs.M68kGlobalLabelStubIndex"/>
         <stubIndex implementation="de.platon42.intellij.plugins.m68k.stubs.M68kSymbolDefinitionStubIndex"/>
         <stubIndex implementation="de.platon42.intellij.plugins.m68k.stubs.M68kMacroDefinitionStubIndex"/>
-        <psi.referenceContributor implementation="de.platon42.intellij.plugins.m68k.refs.M68kReferenceContributor"/>
+        <psi.referenceContributor language="MC68000" implementation="de.platon42.intellij.plugins.m68k.refs.M68kReferenceContributor"/>
         <gotoSymbolContributor implementation="de.platon42.intellij.plugins.m68k.refs.M68kChooseByNameContributor"/>
         <renameInputValidator implementation="de.platon42.intellij.plugins.m68k.psi.M68kRenameInputValidator"/>
         <include.provider implementation="de.platon42.intellij.plugins.m68k.scanner.M68kIncludeFileProvider"/>