Basically with the type/member drop downs, as the document is parsed and an AST is generated, it will update the drop downs once the editor idles. The parsing occurs asynchronously. So if you load a document, it parses, and the drop downs update. Then if you hold a letter, while you are doing so, parsing and updating of the drop down AST range data keeps being put off until you idle in the editor again. This keeps performance fast. But the problem is that while you are moving the caret via the typing, the offset moves, and it uses the older AST offset range data currently in the drop downs to select which type/member it thinks it's in. That's why you might see it be slightly off in that scenario temporarily until the AST range data gets refreshed again.
If you want to put together a new simple sample project that shows the problem happening, we can take a look and debug it to see if there's anything that can be done to help. If you send anything, please email it to our support address and reference this thread. Be sure to rename the .zip file extension so it doesn't get spam blocked. Thanks!