This is likely a Windows-only issue. Try to e-mail a document with an e-mail client set up (at least works with Outlook). => While the user is writing the e-mail, LibreOffice window is unresponsive in the background. Reproduced using LO 6.1 master build / Windows 7.
https://gerrit.libreoffice.org/50476
Mike Kaganski committed a patch related to this issue. It has been pushed to "master": http://cgit.freedesktop.org/libreoffice/core/commit/?id=5874c76371562c3e2d8564b1fb04df1997091d27 tdf#116074: Use modeless dialogs with supporting mailers It will be available in 6.1.0. The patch should be included in the daily builds available at http://dev-builds.libreoffice.org/daily/ in the next 24-48 hours. More information about daily builds can be found at: http://wiki.documentfoundation.org/Testing_Daily_Builds Affected users are encouraged to test the fix and report feedback.
https://gerrit.libreoffice.org/50826
Mike Kaganski committed a patch related to this issue. It has been pushed to "master": http://cgit.freedesktop.org/libreoffice/core/commit/?id=2f061dad7f875f704e3744fc5780c1d145b22e9f tdf#116074: Don't block on sending email interactively It will be available in 6.1.0. The patch should be included in the daily builds available at http://dev-builds.libreoffice.org/daily/ in the next 24-48 hours. More information about daily builds can be found at: http://wiki.documentfoundation.org/Testing_Daily_Builds Affected users are encouraged to test the fix and report feedback.