a checkbox that is writable on the form may return incorrectly for an isEditableField check.

 

1) Create a table with two boolean fields boolA and boolB
2) Create a write ACL on yourtable.boolA with admin overrides = false and script: answer=false
3) navigate to your table and notice that boolA is read only and boolB is not read only.
4) Using the console in your debugger tools, set your frame to gsft_main and exeute the following:
var control = g_form.getControl('boolB');
var fieldGE = g_form.getGlideUIElement('boolB');
g_form.isEditableField(fieldGE, control);
g_form.isReadOnly(fieldGE,control);

Expected: isEditableField should return true, isReadOnly should return false.
Actual: isEditableField returns false, isReadOnly returns true.

Set the actual read only checkbox to read only with a client side method like UI Policy or Client Script.