Task beginsPattern does not work

This is my task config (it is from the github.com/microsoft/monaco-editor): ``` { "label": "Launch Http Server", "type": "shell", "command": "node_modules/.bin/http-server --cors --port 5002 -a 127.0.0.1 -c-1", "isBackground": true, "problemMatcher": { "pattern": { "regexp": "" }, "background": { "beginsPattern": "Starting up http-server", "endsPattern": "Shutting down server" } }, "dependsOn": ["npm: watch"] }, ``` However, the task does not complete:  This is logged escape sequence, it clearly contains the begin pattern: ``` LogService.ts:60 xterm.js: Unbinding from mouse events. LogService.ts:60 xterm.js: parsing data "]633;A]633;P;Task=True]633;P;Cwd=c:\dev\microsoft\monaco-editor]633;B * Executing task: node_modules/.bin/http-server --cors --port 5002 -a 127.0.0.1 -c-1 ]633;C" (190) [27, 93, 54, 51, 51, 59, 65, 7, 27, 93, 54, 51, 51, 59, 80, 59, 84, 97, 115, 107, 61, 84, 114, 117, 101, 7, 27, 93, 54, 51, 51, 59, 80, 59, 67, 119, 100, 61, 99, 58, 92, 100, 101, 118, 92, 109, 105, 99, 114, 111, 115, 111, 102, 116, 92, 109, 111, 110, 97, 99, 111, 45, 101, 100, 105, 116, 111, 114, 7, 27, 93, 54, 51, 51, 59, 66, 7, 27, 91, 48, 109, 27, 91, 55, 109, 32, 42, 32, 27, 91, 48, 109, 32, 69, 120, 101, 99, 117, 116, 105, …] LogService.ts:60 xterm.js: parsing data " " (2) [13, 10] LogService.ts:60 xterm.js: parsing data "[?25l[10:55:09] Starting compilation in watch mode...  [10:55:27] Found 0 errors. Watching for file changes.                                [?25h" (311) [27, 91, 63, 50, 53, 108, 27, 91, 72, 91, 27, 91, 57, 48, 109, 49, 48, 58, 53, 53, 58, 48, 57, 27, 91, 109, 93, 32, 83, 116, 97, 114, 116, 105, 110, 103, 32, 99, 111, 109, 112, 105…