Sorry, this is by design. The tab semantics for Unix terminals is fairly complex (e.g. it can be altered via the ANSI escape sequences and it’s also possible to start overwriting text in the middle of a tab break), so VisualGDB automatically translates all terminal input it receives into a simple 2-dimensional matrix of characters and attributes.
We might be able to add a special attribute tracking whether a group of spaces was created in response to a tab symbol, but realistically we won’t be able to do it until the next major redesign of the terminal logic (that is not on the radar yet), sorry.