We try to keep CMDebug as compatible as possible with CMD, given the limitations and bugs in CMD, the variances in CMD in different versions of Windows, and the thousands of additional features available in TCC-RT.
In the CMDebug Options menu, there is an option to choose either TCC syntax or CMD syntax. (The default for .BAT and .BTM files is CMD syntax.) If you choose CMD syntax, CMDebug will disable the TCC-only commands, internal variables, variable and user-defined functions, and plugins. CMDebug will also set a number of options to maximize CMD compatibility, including emulating a number of (known) CMD bugs.
On rare occasions, you may find batch files that exploit undocumented features (or bugs) in CMD (or are simply badly written) that don't work in CMDebug. If you do, please send those batch files to firstname.lastname@example.org so we can try to emulate the CMD behavior (or at least suggest a better workaround).