I am using Notepad++ version 6.5.3 (Unicode) and have the TabIndentSpaceAlign plugin (version 1.0) installed, and it appears in the drop-down list available from the Plugins menu in the toolbar.
However, Plugin Manager (version 18.104.22.168) does not include TabIndentSpaceAlign in its 'Installed' tab; instead it includes it in its 'Updates' tab, noting that the installed version is 'unknown' and that version 1.0 is available.
Even if I opt to install the reported update and allow Notepad++ to restart, Plugin Manager still insists the plugin is not installed and continues to offer the update.
Any ideas as to what is going on here?
See my answer to the similar issue you raised with regards to PythonIndent.